The mid-Miocene Climatic Optimum (MCO; 16.75–14.5 Ma) was the warmest period during the Neogene and Quaternary, which was followed by a significant global cooling, i.e. the mid-Miocene Climate Transition (MCT; 14.5-13 Ma). During the MCT, global dry land expanded which would have led to an increase in dust release, and may have impacted the paleoclimate evolution. As a crucial climatic factor, aerosols including dust and black carbon during the past were not quantitatively estimated. Here we use a general circulation model, the Community Earth System Model (CESM1.2.2) to simulate the mid-Miocene atmospheric aerosol concentrations and their effects on the North African and South Asian climates. Our results show that the atmospheric dust loading during the mid-Miocene is lower than that of the pre-industrial period, but the atmospheric black carbon concentrations are higher, which is qualitatively consistent with geological records. Such an aerosol scenario leads to a large precipitation increase over South Asia compared to the pre-industrial aerosol pattern, especially during the boreal summer. However, the hydrological change over northern Africa shows the opposite. Aerosols affect regional hydrological response via altering energy fluxes and cloud properties that ultimately lead to increased moisture transport from North Africa to South Asia. The wetter South Asia and direr North Africa agree with geological records during the MCT, which implies that the North African and South Asian climate evolution during the MCT was at least partly due to the change of the atmospheric aerosols associated with dry land expansion.
 

aerosol, paleoclimate modeling, Mid-Miocene Climatic Optimum, Mid-Miocene Climate Transition